136 km SE of Perryville, Alaska

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth, people at rest would likely notice it out to about 27 km (17 mi) from the epicentre. Estimated from magnitude, depth and distance with the intensity equation USGS Did You Feel It? uses; felt reports, where there are any, are the measurement.

How big was it?

This earthquake released about 950 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.0 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 350,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 16,000× the energy of this one
3. Magna, Utah 2020 M 5.7 11,000× the energy of this one
4. This earthquake M 3.0 about 950 lb of TNT

Energy from the Gutenberg–Richter relation (log₁₀E = 1.5M + 4.8), rounded to two figures; bar length is magnitude, which is already a logarithm of energy. Magnitudes of past earthquakes from the USGS catalogue.

For this area

The largest earthquake within 50 km since 2016 was M 8.2 on 2021-07-29 — about 63,000,000 times the energy of this one.

Before 2016, the USGS record lists 14 earthquakes of M5 or more within 50 km; the five largest:

1. 8.2 1938 Semidi Islands, Alaska Earthquake · 41 km WNW of this epicentre Nov 10, 1938
2. 6.9 105 km ESE of Perryville, Alaska · 38 km NNW of this epicentre Nov 17, 1938
3. 6.7 121 km SE of Chignik, Alaska · 48 km NNE of this epicentre Feb 13, 1979
4. 6.2 143 km SE of Perryville, Alaska · 23 km SSW of this epicentre Mar 25, 1927
5. 6.0 98 km ESE of Perryville, Alaska · 43 km NNW of this epicentre Jan 2, 1985

Since 2016: the QuakeIndex catalogue (US, M1.5+), built from the USGS FDSN event service. Before 2016: USGS ComCat, M5+ from 1900. Distances are between epicentres. This is the record, not a forecast.

Where

Epicentre 55.0779, -157.5523. Map © OpenStreetMap contributors.

Aftershocks so far

58 earthquakes have been recorded within 50 km since this one.

1. 3.8 141 km SE of Perryville, Alaska 23:55 UTC
2. 2.3 115 km SE of Perryville, Alaska 15:20 UTC
3. 2.6 142 km SE of Perryville, Alaska 05:51 UTC
4. 2.9 147 km SE of Perryville, Alaska 18:34 UTC
5. 2.7 151 km SE of Perryville, Alaska 17:57 UTC
6. 2.8 171 km SE of Perryville, Alaska 02:53 UTC
7. 2.5 153 km SSE of Chignik, Alaska 23:02 UTC
8. 3.0 Alaska Peninsula 03:51 UTC
9. 2.9 106 km ESE of Perryville, Alaska 04:51 UTC
10. 2.3 129 km SE of Perryville, Alaska 05:47 UTC
11. 3.2 150 km SSE of Perryville, Alaska 13:22 UTC
12. 2.6 144 km SE of Perryville, Alaska 07:02 UTC
13. 2.6 131 km SSE of Chignik, Alaska 08:12 UTC
14. 2.4 120 km SSE of Chignik, Alaska 22:18 UTC
15. 3.0 126 km SE of Perryville, Alaska 19:32 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 01:40 UTC. QuakeIndex does not forecast aftershocks. When USGS issues an operational aftershock forecast it appears on the USGS event page.

On USGS

• The official USGS event page — the source of record for every value above
• Did you feel it? Report it to USGS — reports go to USGS, not to us
• ShakeMap for this event, when USGS has produced one

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.